The present invention relates to a high-speed snapshot function of copying a content in an area of a source-side magnetic disk at a point in time to a corresponding area in a snapshot-side magnetic disk, the content being overwritten by new data after the above-mentioned point in time, and also to host equipment, a switch, and a storage system as means for realizing the high-speed snapshot.
In the prior art of snapshot technology, when a request to write data to the source-side magnetic disk comes from the host equipment, data present in the area is copied to the snapshot-side magnetic disk. After copying data to the snapshot-side is finished, new data is written in the source-side magnetic disk. When the host equipment again issues a request to write data to the source-side magnetic disk, just as mentioned above, data in the specified area is copied to the snapshot-side magnetic disk, and then new data is written to the source-side magnetic disk. This technology is disclosed in U.S. Pat. No. 5,649,152.
The snapshot copy, such as mentioned above, can be controlled by the host equipment or the storage system.
As a method for managing snapshot, there is a technology in which in a case a snapshot is not taken, when data is written from host equipment to an external storage device, data is written in a plurality of storage media to thereby provide a couple of storage areas in which data is stored, and when a snapshot is taken, one of the paired storage areas is used as an area for ordinary access, and the other storage area is used for snapshot. This technology is disclosed in JP-A-2001-306407.